This invention relates to a control system for an alternating-current motor, and more particularly to an adaptive control system for a poly-phase induction (or synchronous) motor.
Speed control means for controlling the speed of an induction (or a synchronous) motor by varying the supply frequency, and voltage control means for controlling the supply voltage as a function of the controlled frequency are heretofore well known. In those heretofore known control systems, however, an adaptive control mechanism, with which a desired performance of the motor is maintained, is not provided.
Therefore, it has been difficult to design a feedback control system of excellent characteristics using a general type induction (or synchronous) motor as the servo-motor. Thus, a direct-current motor or a two-phase induction motor with a control winding has been used as the servo-motor in these control systems.
Although a direct-current motor is expensive and has maintenance difficulties and the amplifier for the control winding of a two-phase motor is inefficient, these disadvantages have been considered inevitable.
Since induction motors and synchronous motors are inexpensive, can stand rough treatment, and can easily be speed-controlled when supplied by a variable frequency power source, it has been desired to use these alternating-current motors as servo-motors in feedback control systems.